Search PubMed⌕ Search

Biomedical subjects

W Timischl

Publications and source records attributed to W Timischl.

8 recordsLinked to original sources
PubMed1987

Geometrical constraints on Bennett's predictions of chromosome order.

Two aspects of the Bennett model are of interest from a mathematical point of view. First there is the question whether Bennett's "ranking method" for predicting the order of chromosomes will always work. The answer depends on the number n of chromosomes: if n is odd, predictions (being not necessarily unique) are possible in most cases. Secondly there is Bennett's procedure for determining the arrangement of chromosomes. It is shown that the method of minimising the perimeter of the polygon obtained by connecting the centromeres is only applicable if the positions of the n centromeres do not deviate too much from an arrangement along a regular n-gon.

Animals↗
PubMed1986

On the process of stabilization in the renewal model: approximations for the time to convergence.

The transient behaviour of the renewal model leading to the stable age distribution is studied for weakly skewed net maternity functions (found in human as well as in some animal populations). The study, which is partly based on heuristic arguments, first provides approximate expressions for the damping constant and the circular frequency (in terms of the moments of the net maternity function) belonging to the principal oscillatory component of the birth trajectory. The time to stability (defined as the time interval after which the principal oscillatory component has become less than a certain fraction of the stable solution) is then determined in two cases: For the genesis model and for a stable population in which the net reproduction rate is reduced to one. The results are applied to a problem which arises in the mass rearing of pest insects.

Animals↗
PubMed1985

Discrimination of taste and preference for sweet in premature babies.

A modified method for registering non-nutritive sucking behaviour with and without taste stimulation enabled us to study taste perception of premature babies. We wanted to study how babies who had no extrauterine taste experience reacted to one or more stimuli with water and 33% glucose. Eight randomly selected healthy newborns (three of them being SGA without further symptoms), exclusively fed by gastric tube, were studied. The mean gestational age at the time of the study was 35.5 weeks. They were studied five times with water and five times with glucose just before feeding. In seven babies the sucking response to glucose was greater than that to water from the first trial onwards. Sucking response increased with repeated glucose stimulation, but remained the same with water stimulation. The eighth baby behaved completely differently. We concluded from our results that premature babies with a postconceptional age of 35 weeks can discriminate between sweet and not-sweet. The greater sucking response to glucose than to water at the first trial implies a genetic factor in the preference for sweet in humans.

Discrimination, Psychological↗
PubMed1982

[The determination of oxygen consumption from temperature measurements with the use of a thermodynamic model ].

A thermodynamic model is described which allows to calculate the oxygen consumption from 4 temperatures as input-variables. These input-variables are: one core-temperature (Tesoph), two skin-temperatures (one at the chest, one at the calf) and the incubator-air temperature. This model is based on the close relationship between oxygen consumption and heat production. The rate of heat production is derived from heat loss to the environment plus heat storage in the body. The data are smoothened by a special mathematical procedure and processed by a HP-85 Computer. Oxygen consumption was synchronously determined by the thermodynamic model and by a conventional method 155 times in four newborns. The flow-through method was used as conventional reference method. The results show that the thermodynamic model yields values for oxygen consumption which are closely related to directly measured values; which indicate the increase in oxygen consumption with activity and decreased environmental temperature; and which follow rapid changes in oxygen consumption of 5 ml/kg per minute. Consequently this thermodynamic model seems suitable to predict the relative changes in oxygen consumption. However the absolute values of oxygen consumption obtained by the model and obtained by direct measurement differ by 5 to 25% the thermodynamic model yielding systematically higher values than the direct measurement. The reasons for this difference are discussed. We demonstrated that a maximum of reliable information can be obtained from a minimal number of measuring sites on the patient by using a theoretical-analytical model.

Body Height↗
PubMed1982

[A thermodynamic model to predict oxygen consumption and peripheral blood flow in the newborn infant. II. Its validity under steady-state conditions].

A thermodynamic model, which allows to predict oxygen consumption and peripheral blood flow from temperature measurements, was tested for its validity in newborn infants. This model is based on the close relation between 1) oxygen consumption and heat production and 2) between circulation and heat convection. In this model 3 temperatures on the patient, 2 temperatures in the environment and geometrical variables (weight, length) are measured and known physiological relations used to calculate oxygen consumption (VO2) and peripheral blood flow (pBF). In 15 newborns the VO2 was synchroneously determined by means of the flow-trough method and the thermomodel. The VO2 and the VO2/kg bodyweight respectively correlated significantly (p less than 0.01) with the directly measured VO2 (correlation coefficients r 0.89 and 0.66 respectively). In 12 newborns the peripheral blood flow was synchroneously determined by means of the impedance plethysmography and the thermomodel. The directly measured peripheral blood flow correlated significantly (p less than 0.001) with the peripheral heat flow (r = 0.73, 34 measurements) and with the peripheral blood flow (r = 0.86, 34 measurements) both obtained from the thermomodel. The values of VO2 and pBF obtained by direct measurement and by the thermomodel are as closely correlated as values which were obtained comparing two conventional methods. These results demonstrate the validity of the theoretical model being suitable for clinical use to continuously predict VO2 and pBF.

Humans↗
PubMed1981

[A thermodynamic model to predict oxygen consumption and peripheral blood flow of the newborn infant (author's transl)].

The continuous evaluation of the oxygen consumption and peripheral blood flow is technically difficult and practically not feasible in the newborn infant. We attempted to assess these two variables by means of a thermodynamic model, where only a set of geometrical variables and a set of temperatures have to be measured. The body is represented by a central cylinder (head, trunk) and a peripheral cylinder (extremities) and the heat flux therein is described by mathematical formulas. Only steady state conditions are considered. From the heat flux "surface leads to environment" the oxygen consumption and from the heat flux "central cylinder leads to peripheral cylinder" the peripheral blood flow is derived. On the patient only one core temperature (rectum) and two skin temperatures--one on the chest and the other one on the calf--have to be measured. The validity of the model was tested in 17 healthy newborns (body weight 1,100-3,850 g) and 6 diseased newborns (body weight 1,500-3,400 g). Comparing the computed oxygen consumption to values from the literature for a similar group showed good agreement. In 7 newborns the calculated oxygen consumption correlated well (r = 0.88, p less than 0.01) with the directly and synchroneously measured oxygen consumption. Indirect proof that the model also gives a reasonable index for the peripheral blood flow was obtained by relating the computed peripheral blood flow a) to values from the literature for a similar group and b) by demonstrating the dependence of the (calculated) peripheral blood flow on the haematocrit (r = -0.58, p less than 0.01).

Humans↗